I was planning on putting a 55i on an EF 88" Extra. I was looking at Cactus's site and I was surprised to see that the 3w-56 is the same horsepower and a little lighter. I would think that the 56 twin would be more like a 40cc single. How do these engines compare to each other. If they are about the same I would prefer the smoothness of the twin.

3W55i
Horsepower: 5.5
Weight: 4.2

3W56
Horsepower: 5.5
Weight: 4.10


Thanks!

The 3w-56 is an awesome engine and will fly the 88" Extra with ease. I'd take it over the 55 in a heart beat.

Hey Mike....first thing that comes to mind for me would be the smoothness like you said, and the cylinder poking out the bottom of an extra cowl, vs a nice baffled install using the stock inlets. I'm sure others will comment on the performance side, and I'm with you, thinking that the single of the same displacement would be a bit more torquey, at the cost of some vibration, but who knows, maybe the install differences would sway you?

Chad

Edit....well there you have it Mike...if you don't know Pat on here, he's one opinion you can certainly trust

Pat,

do you know if there is much of a difference between the straight 56 and the 56CS?


Hey Chad,

Gonna have the SU-31 ready this summer?

I only have experience with two 3w-56 engines, but everyone says the CS is a little stronger. I could not attest to that. I suppose the difference in dollars has more import. The straight 56 is a strong running beast, and will go head to head with anything else in it's size class. Do like Altavillan did and put some cans on it. It really comes to life with a good exhaust system.

Yes'sir, Bless EF for coming out with some planes suited for 4# engines. My 56 is in a EF Yak and I really like the way it flies.
I built a 2 into one header to eliminate the extra cannister weight, so there's no weight penalty. Then I found the correct header length, about 13 3/4" from the exhaust flange. It's happiest with a 23x8 Xoar or NX, with NX being a shade better. 6800 rpm on the NX and 6700 on the Xoar. I back the timing off a tad when I found the correct tune length and it helps smooth out transitions and seams to up rpm's a bit. The stock carb runs well but is a larger body than the one on mine now. Also the stock carb has the needles pointing straight up. The smaller body carb on mine now, weighs a couple oz. less, has a slightly larger venturi 34 or 38/64", (I don't remember exactly) and increases rpm's by quite a bit. I can dig up the carb # if needed. Care in placing the engine mount bolts keeps the needles from being right where you don't want them. Do not buy the engine mount that AI sells, the bolt holes will not fit the planes firewall. I can show pics of my mounting bars.

Alta,
What does your Yak weigh? I would love to see pictures of your set up. Is there a significant power increase with the 2 into 1 pipe?

It weighs under 18# without the pilot and lite batts. Fully loaded with pilot and redundant batts less fuel 18#2 oz.
It's this Yak http://www.rcuniverse.com/forum/m_7385806/tm.htm